Nowadays, there exists a technique for dividing storage devices into groups and distributing and redundantizing user data among storage devices in each group so as to increase the reliability of them as one storage apparatus. For example, a disk array apparatus which is called a RAID (Redundant Arrays of Inexpensive Disks) in which hard disk devices are used as storage devices is known.
In a storage apparatus of the above mentioned type, typically, immediately after user data has been written into a storage device, the user data is again read out of the storage device so as to confirm whether the read user data matches the written user data. In the storage apparatus, the possibility that the user data is read out of the storage device immediately after it has been written into the storage device is higher than that in an archive apparatus and the validity of the user data which has been just written into the storage device is secured by confirming matching between the written data and the read data in the above mentioned manner.
On the other hand, in some cases, user data which has been recorded, for example, in a hard disk may turn to invalid data owing to degradation of magnetism of the hard disk and may be detected as invalid data through CRC (Cyclic Redundancy Check) and inspection of a block ID. Therefore, a patrol diagnostic technique for detecting in advance data that has turned to invalid data (hereinafter, referred to as “bad data”) although it is written into a storage device is known.
Japanese Laid-open Patent Publication No. 11-24956 and Japanese Laid-open Patent Publication No. 2008-27240 are examples of related art.
However, an existing patrol diagnostic technique has such a problem that in the case that the whole of a LUN (Logical Unit Number) is set as a patrol object (an object to be patrolled), much time may be taken to patrol the LUN. In the following, the above mentioned problem is specifically described. A storage apparatus includes more areas into which nothing is written than areas into which user data is written in response to a request from a host apparatus. However, the storage apparatus may not recognize a location in a storage device into which the user data is written. Thus, in the case the whole of the LUN is set as the patrol object, it may become unavoidable to patrol all of the storage devices included therein and hence much time may be taken to patrol the LUN. In particular, in the case that a new storage apparatus has been introduced, much time may be taken to patrol all of the storage devices included in the newly introduced storage apparatus in spite of the fact that areas with no user data written have a majority and hence patrolling may not be performed efficiently.
In addition, in the case that the whole of the LUN is set as a patrol object, patrol diagnosis is intermittently performed at such a timing that it is performed, for example, once every several seconds so as not to adversely affect input-output (I/O) performed using a host apparatus. Thus, the time taken until patrolling of the LUN is completed may be further increased.
Under the above mentioned circumstances, how patrolling is efficiently performed in a short period of time becomes a serious problem to be solved in the case that the whole of each storage device is set as a patrol object.